Lots -- we mean lots! -- of bacteria on our skin

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In a fun study published online today in the journal Science, researcher Elizabeth Costello and colleagues at the University of Colorado at Boulder and at Washington University in St. Louis report on their cataloging of the 100 trillion microbes that reside on our insides and outsides by sampling 27 different spots on the human skin.

Ears. Mouth. Underarms. Private parts. More. This is an update on an earlier analysis by the same group, conducted by taking samples from several healthy adults (three females, six males), none of whom had taken antibiotics for the prior six months.

The new analysis, we’re told, underscores the fact that body site is a better predictor of what will be growing where than the particular identity of a person or a person’s age. (There are individual differences, however, as well as differences depending on when the samples were taken.)

Sites of especial diversity: The index finger, back of knee, forearm, palm and sole of foot.

Sites of less diversity: The forehead.

Sites where Staphylococcus bacteria seemed to thrive: armpits and soles of feet.

Sites where Corynebacterium species seemed to thrive: navel and backs of knees.

Lactobacillus species were the dominant microbes on the labia minora.

It seems the bacteria just plain seem to like those spots: The scientists conducted experiments in which they took bacteria from one spot on a body and placed them on another spot that had been disinfected. Alas, the microbes often did not thrive in the new locations. Greasy sites were particularly specific as to the critters they harbored. ‘For example,’ the press materials inform us, ‘forearm microbes did not grow as well on the forehead, but forehead microbes grew just fine on the forearm.’

Lord knows what it all means, but the scientists hope their cataloging will provide a baseline, so that what happens during disease can be better understood.

Here’s a write-up of the findings BBC News. And a blog at Technology Review.

-- Rosie Mestel